The museum uses images and audio and video from its permanent collection to tell the 9/11 story, filled with first-person accounts from survivors, first responders and witnesses.

There are audio recordings from phone calls on that day, oral histories from survivors and eyewitnesses and graphic photographs and video snippets arranged in chronological order, reports the Associated Press.

Joe Daniels, the museum's president, said the project's organizers were sensitive to the nature of what they were presenting and took steps such as leaving it up to viewers as to whether they wanted to take closer looks at specific photographs and videos or listen to particular bits of audio, some of which is quite graphic, reports the news outlet.

"We are the institution that needs to preserve the history of what happened," Daniels said. "That means taking on some of the difficult material. That means reminding people of some of the difficult stuff."

AP

People who lost loved ones that day are supportive of the site. Charles G. Wolf, who lost his wife, Katherine Wolf, at the World Trade Center, said the timeline was a positive thing.

"We don't want it to be sugarcoated," Wolf said. "We want people to understand what it was like."

Alice Hoagland, who lost her son Mark Bingham on United Airlines Flight 93, told AP she hadn't seen the timeline yet but that "it's a tremendously good teaching tool for people who want to understand the events of that day."

The chronology starts at 5:45 a.m. showing photographs of two hijackers passing through airport security in Maine for a flight to Boston, where they would board American Airlines Flight 11. It ends at 8:30 p.m. with President George W. Bush addressing the nation.

Viewers can use social media including Facebook and Twitter as well as e-mail to share links to the site and to particular photos and videos.

On the museum's website, a warning reads, "Due to the nature of events related to the Sept. 11 attacks, the timeline contains some graphic images and sensitive content. Parents may want to first review the site before sharing it with young children."